Difference characteristics and main controlling factors in gas-bearing of coal seams in Liupanshui Area

The Liupanshui Area is an area with particularly developed coal seams and complex geological conditions in southern China.In recent years, the results of coalbed methane test production in this area is good,and the exploration progress is obvious. Finding out the gas-bearing characteristics of coal seam in this area is helpful to deepen the understanding of the formation and storage rules of coalbed methane, and improve the success rate of exploration. Based on the actual drilling data of several CBM parameter Wells in the study area and a large number of gas components, gas content, isothermal adsorption and basic analysis data of coal and rock obtained from the test of coal and rock samples, the spatial difference characteristics of coal bed gas content in Liupanshui area are analyzed, and the key geological controlling factors of coal seam gas content difference are discussed. The analysis results show that the coalbed methane component in the area is dominated by methane, and heavy hydrocarbons are prone to abnormalities in the middle coal rank stage. The heavy hydrocarbon components are mainly ethane. Hydrocarbon gas and nitrogen are highly linearly negatively correlated, and locally high abnormal nitrogen mainly comes from the atmosphere. There are various types of coal-bed methane genesis, and the critical value of vitrinite reflectance at which the genetic type changes is about 1.70%. The gas content and Langmuir volume of coal seams are generally high. The stage of low and high coal rank is generally adsorbed gas, while the part of coking coal seams of medium coal rank is characterized by free gas. The adsorption capacity and gas content of coal seam are affected by both accumulation geological factors and preservation geological factors, and there are certain differences on the plane. The main factors that affect the difference in adsorption capacity are the degree of coal metamorphism and the temperature and pressure environment, and the main factors that affect the difference in gas content are the degree of coal metamorphism, buried depth and structure. Generally speaking, the variation of Langmuir volume in the same exploration area is relatively less than that of gas content. Affected by the accumulation of geological factors, the adsorption capacity and gas content are also different among different coal seams in the vertical direction. The main influencing factors are the organic microscopic composition of coal and coal quality.